Composite laser beams are substantially colinear light beams respectively containing light beams from a plurality of separate lasers, each laser emitting its own relatively narrow band of wavelengths. Typically each of the constituent lasers emits a different wavelength. Accordingly the resulting composite beam can be referred to as a multiwavelength composite laser beam.
Multiwavelength composite laser beams are particularly useful in laser isotope separation. With appropriate choice of wavelengths, a multiwavelength composite beam shone through an isotopic mixture can effect isotopically selective, multiple-step excitation or even photoionization. Typically the composite beam includes at least one narrow band wavelength component for selectively exciting atoms or molecules comprising the desired isotope and a plurality of additional wavelength components for further exciting the atoms or molecules to even higher states. The selectively excited components of the mixture are then separated from the non-excited components by electrical, electromagnetic, chemical or mechanical means. See, for example, U.S. Pat. No. 3,443,087 issued to Jean Roieux et al; U.S. Pat. No. 3,772,519 issued to Richard Levy et al; British Pat. No. 1,284,620 issued to Karl Gurs; and U.S. Pat. No. 3,996,470 issued to James Keck.
For efficiency in isotope separation, the optical system used in generating the multiwavelength composite laser beam must meet a number of stringent requirements. First, such systems should contain a minimum number of lossy components. Typically they require high intensity laser beams to effect the desired separation. Lossy components, such as dichroic elements, greatly restrict the level of deliverable intensity. Second, such systems should produce a composite beam having a high degree of colinearity among its constituent components. This requirement arises because the different wavelength components must act on the isotopic mixture substantially simultaneously and because extremely long paths, typically folded, are required to fully utilize the laser output. Third, such systems should be capable of a high degree of synchronism. As previously indicated high power lasers capable of acting together are needed. In typical applications pulsed lasers are used and care must be taken to ensure that they pulse in synchronism.
Prior art arrangements for producing high power, composite laser beams typically comprise a plurality of high power lasers, one for each desired wavelength, and a beam combining system comprised of dichroic elements, rotating optics or beam splitters. See, for example, U.S. Pat. No. 3,521,068 issued to Armstrong et al. Such systems are less than satisfactory for isotope separation because they typically utilize lossy components and because of the difficulties in accurately collimating and synchronizing so many different lasers.